Estrogens are female sex steroids that have a plethora of effects on a wide range of tissues. These effects are mediated through two well characterized intracellular receptors: estrogen receptor alpha and beta (ERalpha and ERbeta, respectively). Because of their high structural homology, it has been argued whether these two receptors may elicit differential biochemical events in estrogen target cells. Here we examine the effect of 17beta-estradiol-dependent activation of ERalpha and ERbeta on neurite sprouting, a well known consequence of this sex hormone action in neural cells. In SK-N-BE neuroblastoma cells transfected with ERalpha or ERbeta, 17beta-estradiol induces two distinct morphological phenotypes. ERalpha activation results in increased length and number of neurites, whereas ERbeta activation modulates only neurite elongation. By the use of chimeric receptors we demonstrate that the presence of both transcription activation functions located in the NH2-terminus and COOH-terminus of the two ER proteins are necessary for maintaining the differential biological activity reported. ERalpha-dependent, but not ERbeta-dependent, morphological changes are observed only in the presence of the active form of the small G protein Rac1B. Our data provide the first clear evidence that, in a given target cell, ERalpha and ERbeta may play distinct biological roles and support the hypothesis that 17beta-estradiol activates selected intracellular signaling pathways depending on the receptor subtype bound.